Vijay - roaming profile and new server setup

[Vijay Kumar]

Hi,

We are having a samba server running samba :2.2.3a 
The current version is above 3.0 
The old samba server has roaming profile enabled and this is a major
problem as there are GB's of emails and data downloaded to and from the
server daily. 

a) How can I disable roaming profile and have the profile locally stored
   on the users machine ? How can I achieve this ? 
     i) If the users are logged in and I disable the roaming profile the
         machine will try to write back the profile to the server. This
         may generate some error.  
     ii) If the users are not logged in, they will not be able to
          download their emails and data and hence I cannot disable the
          roaming profile. 
     How should I solve this issue ?

b) What is the threshold as far as the number of machines/users on
    a server is concerned ? I now need to setup a new server with about
    400 machines. Is there any statistical data available ? How many
    machines/users can Samba support and what precautions shoudl I take
   while setting up the new server ? 

c) What tests should I run before i deploy it in the network ? Any
    suggestions ? 

I have not worked on samba earlier. Kindly help. 

Regards,
Vijay Kumar.